@
ramius...
If you think is easy to design a machine with dynamic gpu, you should get one with thunderbolt and buy a egpu and try the same thing on it, and while you are using a program that takes advantage of the egpu, try unplugging the thunderbolt cable and see what happens...
Obviously the way the Surface Book was designed take this into consideration and prevents the user from detaching when the gpu is in use. This way avoids crashes, corruption and bluescreens.
I understand your disappointment but that is just the way it is right now.
Luckily in my line of work I use the igpu for my 3D and cad designs and the detaching limitation is not present, I set it to only use the dgpu for games and certain apps.
My only issue is that I can't select UWP apps manually to force them to use igpu or dgpu